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Analyse the Structure of DNA

In this worksheet, students will learn the terminology used to analyse DNA's many different formats, explain the process of protein synthesis using DNA, and how genetic mutations can impact our bodies.

'Analyse the Structure of DNA' worksheet

Key stage:  KS 4

GCSE Subjects:   Biology: Single Subject

GCSE Boards:   OCR 21st Century

Curriculum topic:   You and Your Genes

Curriculum subtopic:   What is the Genome and What Does It Do?

Difficulty level:  

Worksheet Overview

QUESTION 1 of 10

We are our DNA! As this chemical is what all genetic information is made up of.

 

Held in our cell nuclei, it’s a long chain of tightly wound-up coded instructions which cells unravel, read and use to make proteins.

 

When cells want to make a certain protein, they read DNA in chunks called genes that code for a specific sequence of amino acids.

 

 

Like proteins, DNA is also a polymer but of repeating nucleotides- a group made of a phosphate group on a sugar attached to a nitrogenous base, linking together to make the double helix.

 

There are 4 different bases, A, T, C, G, and they’re very specific about who they pair with:

 

Adenine with Thymine and Cytosine with Guanine

 

These groups are complementary base pairs, and they are joined by weak hydrogen bonds, linking the 2 double helix strands in the middle!

 

 

 

So far, we have only said that DNA codes for proteins. This is not entirely true, because there are two types!

 

- CODING DNA are the genes the cells read and makes proteins from

 

-NON-CODING DNA are like on-off switches for coding DNA- they control gene expression by telling the cell to use or ignore certain genes, making sure we only get the proteins we need.

 

 

So making a protein has two stages: TRANSCRIPTION of DNA (in the nucleus) and TRANSLATION (in the cytoplasm):

 

Transcription:

1. The cell reads the genes to get the amino acid order. But DNA is too big to get out of the nucleus to build the protein so it uses a messenger instead!

 

2. An enzyme temporarily breaks the weak hydrogen bonds and unzips the double helix and uses one side as a template to make a copy of the genes there, with this new copy being called mRNA.

 

3. mRNA travels out into the cytoplasm and carries the code to the site of protein synthesis- an organelle called a ribosome

 

Translation:

4. As the ribosome reads the mRNA, 100s to 1000s of amino acids are brought in and joined in the sequence the genes state, making the initial protein chain.

 

After protein synthesis, the polypeptide then folds into a specific 3D structure that makes the protein suitable for its function, like an enzyme and its active site.

 

 

But change happens, and when the order of bases changes in our genes, we call this a mutation.

 

Mutations can, therefore, change proteins through our DNA, but usually, their function is preserved and little difference is seen in our phenotypes.

 

But rarely if enough of the coding and non-coding DNA is changed, the protein’s shape can be altered so much that it can’t do its job, like an enzyme without a working active site.

Put these terms into size order, starting with the largest:

 

Column A

Column B

1. (Largest)
Genome
2.
Double Helix
3.
Gene
4.
Nucleus
5. (Smallest)
Nucleotide

Label the picture of the nucleotides below: 

 

Column A

Column B

1. (Largest)
Genome
2.
Double Helix
3.
Gene
4.
Nucleus
5. (Smallest)
Nucleotide

Which of these possible combinations of DNA bases (Adenine, Guanine, Cytosine and Thymine) are correct?

How many of these statements are true about genes?

 

They give instructions to cells about amino acid sequences

They're small sections of the double helix

They control what proteins are made by a cell

Match the terms below

Column A

Column B

Coding DNA
Controls gene expression
Non-coding DNA
a gene that gives instructions about a specific se...

True or False:

 

'A mutation is a change to DNA that alters how we look'

TRUE or FALSE

What is the role of mRNA?

TRUE or FALSE

What are the two stages of protein synthesis?

Transcription THEN Translation

Translation THEN Protein Folding

Translation THEN Transcription

Protein Folding THEN Transcription

Describe the process of translation in protein synthesis, including the sites of action in the cell and the final result.  

[7 marks]

Being made of many subunits called nucleotides, DNA is considered a what?

  • Question 1

Put these terms into size order, starting with the largest:

 

CORRECT ANSWER

Column A

Column B

1. (Largest)
Nucleus
2.
Genome
3.
Double Helix
4.
Gene
5. (Smallest)
Nucleotide
EDDIE SAYS
This is an important concept to appreciate, as if you understand this question, you have a good grip on how DNA is structured. The largest term here is the nucleus, which acts as the cell\'s storage house of DNA. All these other terms refer to zooming in on the DNA in the nucleus more and more closely, the entire bunch of genetic information being our genome. When the genome is unravelled, we see its DNA exists in as two linked strands in a swirl called the double helix. Number 4 is a gene and the smallest term is a nucleotide, but to learn more about these, press on with the next set of questions!
  • Question 2

Label the picture of the nucleotides below: 

 

CORRECT ANSWER
EDDIE SAYS
The arrangement of a nucleotide is important because how it bonds gives DNA it's double helix shape. On the outside is a phosphate group, which is linked to a corner of a 5 sided sugar called a pentose sugar. The sugar then bonds to a base- depending on the nucleotide, this could be A, T, C or G, which then sticks out into the middle of the double helix, waiting to hydrogen bond to a base from a nucleotide from the opposite strand!
  • Question 3

Which of these possible combinations of DNA bases (Adenine, Guanine, Cytosine and Thymine) are correct?

CORRECT ANSWER
EDDIE SAYS
When the bases hydrogen bond in the center of the double helix, Adenine can only join to Thymine, and Cytosine can only join to Guanine. However, the initials can be switched around, for example both CG and GC are acceptable, as are TA and AT.
  • Question 4

How many of these statements are true about genes?

 

CORRECT ANSWER
They give instructions to cells about amino acid sequences
They're small sections of the double helix
They control what proteins are made by a cell
EDDIE SAYS
ALL TRUE! So, do you think you have a good grasp of all the definitions in this topic? Zooming in on the DNA more and more closely, a piece of its double helix is a gene, which acts as coded instructions to cells in how to make a specific protein. They do this by relaying a certain sequence of amino acids, making sure the correct combination is put together so the right protein is made for that cell by that cell.
  • Question 5

Match the terms below

CORRECT ANSWER

Column A

Column B

Coding DNA
a gene that gives instructions ab...
Non-coding DNA
Controls gene expression
EDDIE SAYS
So it\'s important that we know that DNA does not always = proteins! Coding genes do what we know already and have a specific sequence of nucleotide bases that the cell reads and joins a certain set of amino acids from. But a lot of genes are actually instructions for other genes and aren\'t connected to amino acids at all! Non-coding DNA control which coding genes the cells reads and doesn\'t read, making it the controller of GENE EXPRESSION or gene visibility, as all cells have all the possible genes, but each cell uses different wants to only make the combinations of proteins they need for their function! If it wasn\'t for non-coding DNA, we may be a frog or have 2 hearts, all stopped because we have an on-off switch for parts of our DNA!
  • Question 6

True or False:

 

'A mutation is a change to DNA that alters how we look'

CORRECT ANSWER
TRUE or FALSE
EDDIE SAYS
This one was tricky but remember the intro! It\'s true that a mutation is when a gene changes- this can be natural but can also be caused by exposure to chemicals like radioactive toxins or cigarettes! They can sometimes be beneficial, sometimes dangerous, BUT often have no impact. So it is very RARE that a mutation has an obvious effect on our appearance or our PHENOTYPE.
  • Question 7

What is the role of mRNA?

CORRECT ANSWER
EDDIE SAYS
Here, we're tackling one molecule in the whole protein synthesis process. mRNA stands for messenger RNA as it carries a single-stranded DNA copy called RNA out of the nucleus and into the cytoplasm, where a ribosome sits waiting to decode the nucleotide bases in the RNA so it can start bringing in amino acids and making proteins. This may be a completely different way of looking at both genetics and proteins, but don't worry if it's confusing at first, stick with and just practise practise practise! The best tip is to get lots of different diagrams and pictures from textbooks and Google to help you visualise all these new terms and processes, and I'm sure you'll get it in no time!
  • Question 8

What are the two stages of protein synthesis?

CORRECT ANSWER
Transcription THEN Translation
EDDIE SAYS
Protein synthesis is transcription, THEN translation THEN protein folding as a part of translation!!! Think about it this way, transcribing is like when a secretary used to type while her boss was speaking so she could collect his instructions in a universally readable way- she was a transcriber! So we first have to write up DNA into a format that both the cell and the ribosome can read clearly, making mRNA, so transcription comes first. Then it's clearer that translation is second as we're taking this DNA copy and the ribosome is trying to translate all the instructions into an actual amino acid chain!
  • Question 9

Describe the process of translation in protein synthesis, including the sites of action in the cell and the final result.  

[7 marks]

CORRECT ANSWER
EDDIE SAYS
Many people find protein synthesis very confusing and a lot to remember, but as long as the student keeps breaking it all down into key steps, they'll find it a lot simpler. This question is an example of when a student might get a 6-8 marker asking them to describe a specific process, and here we've chosen to talk about translation. Here's how to approach giving marks in this question: So, a small summary is that translation is the second of two steps in making proteins- here, a structure in the cytoplasm (main area in the cell) called a ribosome reads the messenger DNA sent from the nucleus (DNA storage area) to put amino acids in a specific order to make a unique protein. The easiest marks come from ANSWERING THE QUESTION which is where many students stumble when they're panicked and nervous. The question asks them to state where the process is taking place and what the final result is, so the first marks come from mentioning that translation happens in the RIBOSOME IN THE CYTOPLASM. Next, the student needs to say what happens at the ribosome and define mRNA, either by explaining its role as a messenger or by saying that it's a copy of one side of the double helix, giving the student up to 2 marks. Then for 4 possible marks, the student has to explain the final steps in turning DNA into a protein. They should say that the ribosome reads the specific instructions given by the DNA and that amino acids are then brought in that same stated order to be joined in a unique sequence, giving us that specific protein chain. If the student puts that protein folding takes place, please discount this as this process does not involve genetics anymore and is about the amino acids in the chain interacting with one another, so protein folding is not a part of protein synthesis, although the protein isn't ready for its job until it has become a 3D folded shape. For the pupil, here are some tips about answering these types of long questions and how to think about them: - Remember that the examiner has a mark scheme with bullet points telling them to look out for keywords, so always mention key definitions or terms that you know your teacher has used non-stop in this topic because that'll get you very far on its own. - Then understand that any long processes can always be broken down into simple steps to remember, don't be intimidated by what the examiner or the teacher might expect, and remember that it's all doable as long as you have worked hard beforehand.
  • Question 10

Being made of many subunits called nucleotides, DNA is considered a what?

CORRECT ANSWER
POLYMER
EDDIE SAYS
How did you find this question? The smallest form of DNA if its nucleotides- little building blocks that bond together to form the iconic DNA spiral shape.
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